This invention relates in general to the testing of glazing, and more particularly, a blast load simulation system for testing of glazing, such as glass windows, under various conditions.
One of the major causes of injury and loss of life in structures subjected to blast loading is the glass windows. Common window glass is annealed glass. When annealed glass is subjected to impact loads such as the one generated by a blast, it breaks into relatively large shards with sharp cutting edges. This is responsible for most of the injuries incurred in explosions. In the tragic bombing of the Alfred P. Murrah Federal Building in Oklahoma City in April 1995, more than 75% of the injuries sustained by those who survived in the area surrounding the building were due to flying shards of glass.
Recent research has been exploring the use of high-strength glazing materials such as polycarbonates, laminated glass and tempered glass. Tempered glass fractures at higher pressure levels than annealed glass, and it breaks into small cubed-shaped fragments. The small fragments are presumed to be less lethal. However, the capacity of tempered glass to resist higher pressure levels means that, when the glass fails, the broken pieces have far more energy, and thus become far more lethal. Also, due to their capacity to resist higher blast pressure, tempered glass windows can transfer far greater loads to the structure""s frame, thereby increasing the possibility of the structure""s collapse. To preserve the advantage of a tempered glass window fracturing in small cube-shaped pieces and to reduce its capacity to withstand high blast pressures, researchers at Sandia National Laboratories have proposed various ways of inducing early onset of fracture in tempered glass at lower pressure levels. They have carried out a limited number of tests (using explosives of different sizes) to verily their concept.
Currently, the test facility to carry out these tests is either a shock tube or an open-air arena. The ASTM Standard F1642-96, Standard Test Method for Glazing and Glazing Systems Subject to Airblast Loadings states,
xe2x80x9cOpen air arenas should be sited on clear and level terrain. The Test facility shall be situated, and be of sufficient size, to accommodate the detonation of the required amount of explosives to provide the desired peak positive pressure and positive phase impulse. The test director shall ensure that potential environmental impact issues are determined and resolved prior to testing. The test director shall ensure that testing is conducted at ambient temperature in accordance with section I.1xe2x80x9d.
Section I.1 specifies the ambient temperature as 75xc2x120xc2x0 F. Clearly, qualification with the above testing facility is very expensive. The main obstacle hampering the development of standardized tests for various conditions for glazings, such as glass windows, for blast loading continues to be the limitations imposed by the need to test for explosions of different characteristics.
It is an object of the invention to provide a realistic, simple, safe, and economical physical simulation technique for testing glass panels under various conditions.
It is another object of the invention to provide a technique that can generate pressure shocks simulating blasts of different magnitudes and durations.
It is yet another object of the invention to provide a simulation system that can be used to research the capacity of various glazing as well as other panels to resist blast loading.
It is still another object of the invention to provide a simulation system that can also be used to develop standardized tests for structural elements such as walls, panels, glazing and glass windows subjected to blast loads.
It is still yet another object of the invention to provide a simulation system that can be used to verify computer models.
It is another object of the invention to provide a simulation system that can be used to locally test and quality the sensitivity of glass windows for various environmental conditions, such as temperature.
This invention relates to a blast load simulation system for testing of glazing, such as glass windows, under various conditions. The system comprises a glazing having two surfaces, a membrane for covering one of the two surfaces of the glazing, and means for delivering an impulse with a given characteristic to the glazing through the membrane.
A method of testing glazing against blast loads comprises the steps of:
a) providing a membrane and a glazing with an airtight chamber formed therebetween;
b) filling the airtight chamber with a fluid medium; and
c) delivering an impulse with a given characteristic to the glazing through the membrane.
Various objects and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawings.